From digging into the iOS 8 docs that are available as of Sept 9th 3:30pm there is no mention of developer access to the NFC controller to perform any NFC operations; that includes reading tags, writing tags, pairing, payments, tag emulation... Given its an NXP controller the hardware has the capability to perform these features. They did mention a 3rd party app for the watch that allowed a hotel guest to open their room door with NFC. This is a classic use case for NFC and gives some indication that the NFC controller will be open to developers at some point. Remember, the watch is not supposed to be released until Q1 2015. So for now I'd say it's closed but will be open soon. Given the 'newness' of contactless payments for the general US consumer and the recent security breaches its not surprising Apple wants to keep this closed for a while.
Disclosure: Im the CEO of GoToTags, an NFC company with obvious vested interest in Apple opening up NFC to developers.
--- Correction & Update ---
The hotel app actually uses Bluetooth, not NFC. NFC is still often used for door unlocking, just not in this one example. NFC could be used if the watch has an open NFC controller.
I do know that Apple is aware of all of this and is discussing this with their top developers and stakeholders. There has already been massive negative push back on the lack of support for reading tags. As often the case in the past, I expect Apple to eventually open this up to developers for non-payment related functionality (reading tags, pairing). I do not think Apple will ever allow other wallets though. File sharing will likely be left to AirDrop as well.
--- Update on March 23rd 2016 ---
I am continually asked for updates about this topic, often with people referencing this post. With Apple releasing the iPhone SE, many are again asking why Apple has not supported tag reading yet. In summary Apple is more focused on Apple Pay succeeding than the other use cases for NFC for now. Apple could make a lot of money from Apple Pay, and has less to make from the other uses for NFC. Apple will likely open up NFC tag reading when they feel that consumer trust and security with NFC and Apple Pay is such that it wont put Apple Pay at risk. Further information here.
--- Update on May 24th 2017 ---
A developer in Greece has hacked the iPhone 6s to get it to read NFC tags via the NFC private frameworks; more info & video. While this isn't a long term solution, it provides some guidance on some outstanding question: Is there enough power in the iPhone's NFC controller to power an NFC tag? Looks like the answer is yes. From initial testing the range is a few cm, which isn't too bad. It might also be the power is tunable; this is being investigated at this time. The implications of this are significant. If the older model phones do have enough RF power for tag reading/writing, then when Apple does open up the SDK it means there will be 100Ms of iPhones that can read NFC tags, vs the case where only the new iPhones could.